Hello all, I have about four dozen negative voltage regulators (7906's and 7912's, I believe) that I found in the junk box. I really don't have a need to regulate negative voltages, but postive ones would be nice! Is there any way I could use these for postive voltage regulation, without a prohibitive amount of extra circuitry? I understand the best thing would be to have postive voltage regulators, but I just hate to see a good part go to waste .

The only difference between a positive and negative regulator involves which side of the circuit is held at a constant reference level... A negative regulator works 'upside down' by adding a variable series resistance to the negative leg of the circuit.

This is not a problem for a simple circuit that doesn't care about an absolute ground reference, like pilot lights or an LED display. For something like a low-level preamp that doesn't draw much current you can bypass the negative leg with a series capacitor so the AC signal component will continue to see a common ground. You can also add an 'NPN wrap-around' pass transistor to increase the current capacity.

With that said, I wouldn't trust a work-around that doesn't have a true DC ground reference, no matter how clever, as a power supply for anything of value. Considering how cheap TO-220 regulators can be found, better you should keep the negative regulators in the junk box against the day you decide to tinker with op amps that need a split power supply.

- AC5UP

Logged

Have you considered how many wireless devices are in simultaneous use near PyeongChang, South Korea? The TV coverage alone requires thousands. Then add in the cell phones. Talk about a pileup......!

Copyright 2000-2018 eHam.net, LLC
eHam.net is a community web site for amateur (ham) radio operators around the world.
Contact the site with comments or questions.
WEBMASTER@EHAM.NETSite Privacy Statement